Electric vehicles are widely considered an answer to global air pollution from fossil fuel vehicles. With the exception of the Tesla Model S, however, most electric vehicles cannot travel 100 miles on a full charge. Tesla buyers pay a significant premium for the larger battery packs needed to travel longer distances. Even then, battery vehicles typically must be recharged for hours before they're ready to roll again—something that makes a long trip a chore.
Wireless charging on roadways (known as wireless power transfer (WPT)) has been proposed to address the limited travel range of electric vehicles. Wireless charging uses the following laws of physics: (a) a wire carrying an electric current produces a magnetic field around the wire (Ampere's Law); (b) a coil intersecting a magnetic field produces a voltage in that coil (Faraday's Law); and (c) electromagnetic power transfer between electrical circuits across an air gap can be achieved using magnetic field coupling at resonance (Tesla's Law). Based on these laws, wireless power transfer (WPT), uses a power supply providing alternating electric current in a primary charging coil embedded in a roadway to produce a time-changing magnetic field. The variable magnetic field induces an electric current (producing a magnetic field) in a secondary solenoid winding mounted under a vehicle floor. The induced alternating current and voltage are then rectified to direct current (in an inverter) to recharge an onboard battery or other energy storage device. When a transmitter radio frequency magnetic field matches the receiver frequency, the inductive power transfer (IPT) is called “magnetic resonance”.
While WPT has been effective in powering buses of known battery capacity over known routes, it has not been applied to powering electric or hybrid vehicles having different battery capacities and charge levels over varying routes in the presence of fossil fuel-powered vehicles.